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The  Hydration  of  Sodium  Monometaphosphate  to 

Orthophosphate  in  Varying  Concentrations 

of  Hydrogen  Ion  at  45°  Centigrade 


. 


OP  7  A 


DISSERTATION 

Submitted  in  partial  fulfilment  of  the  requirements 

for  the  degree  of  Doctor  of  Philosophy  in 

the  Faculty  of  Pure  Science  of 

Columbia  University. 


BY 

SAMUEL  J.  KIEHL,  A.  B. 

NEW  YORK  CITY 
1921 


The  Hydration  of  Sodium  Monometaphosphate  to 

Orthophosphate  in  Varying  Concentrations 

of  Hydrogen  Ion  at  45°  Centigrade 


DISSERTATION 

Submitted  in  partial  fulfilment  of  the  requirements 

for  the  degree  of  Doctor  of  Philosophy  in 

the  Faculty  of  Pure  Science  of 

Columbia  University. 


BY 
SAMUEL  J.  KIEHL,  A.  B. 

NEW  YORK  CITY 
1921 


DEDICATED 

TO 
LOUELLA  SOLLARS  KIEHL, 

my  wife, 
whose  sympathetic  interest  has  been  an  inspiration. 


ACKNOWLEDGMENT. 

To  Professor  Hal  Trueman  Beans  at  whose  sug- 
gestion this  problem  was  undertaken,  the  author  wish- 
es to  express  his  sincere  thanks  for  helpful  guidance 
constantly  received  throughout  the  progress  of  the 
entire  investigation. 


THE  HYDRATION  OF  SODIUM  MONOMETAPHOS- 

PHATE  TO  ORTHOPHOSPHATE  IN  VARYING 

CONCENTRATIONS  OF  HYDROGEN  ION 

AT  45°  CENTIGRADE. 


The  hydration  of  metaphosphoric  acid  to  orthophosphoric 
acid  or  a  metaphosphate  to  the  orthophosphate,  as  NaPO3  + 
H3O  -»  NaH2PO4,  has  attracted  the  attention  of  chemists  ever 
since  the  epochal  work  of  Graham1.  Much  work  has  been 
done  but  the  problem  is  not  completely  solved.  Graham  was 
aware  of  some  of  the  difficulties  to  be  encountered.  In  his  work 
he  states,  "The  problem  is  therefore  environed  with  difficul- 
ties." These  difficulties  seem  to  be  twofold : — First,  metaphos- 
phoric acids  or  their  salts  are  not  well  understood.  It  is  known 
that  polymers  exist  the  preparation  of  which  has  not  been 
thoroughly  investigated  and  the  decision  as  to  their  forms 
has  been  based  mainly  upon  their  methods  of  preparation  or 
empirical  formulae  rather  than  upon  experimental  evidence. 
Different  polymers  present  different  problems  of  hydration. 
Second,  the  rate  of  hydration  must  be  ascertained  by  the  meas- 
urement, at  intervals,  of  either  the  concentration  of  the  meta- 
phosphate left  unchanged  in  the  solution  or  the  concentration 
of  the  orthophosphate  formed  during  the  progress  of  the  reac- 
tion. On  account  of  the  widely  differing  solubilities  of  the 
polymeric  forms  of  the  metaphosphates,  the  direct  determina- 
tion involving  an  actual  separation  of  the  orthophosphoric  acid 
from  the  meta  is  by  no  means  easy,  especially  when  pyrophos- 
phoric  acid  is  formed  as  an  intermediate  product.  This  sepa- 
ration is  actually  necessary  in  order  to  study  the  factors  influ- 
encing the  hydration. 

So  to  understand  better  this  reaction  the  two  above  men- 
tioned difficulties  must  be  overcome  as  far  as  possible.  This 
requires,  as  a  basic  consideration,  that  a  definite  polymer  be 
prepared  and  its  hydration  studied.  Furthermore,  the  definite 
polymer  must  be  readily  and  quantitatively  separable  from  the 
substances  formed  during  the  hydration. 


Phil.  Trans.  123,53  (1833). 


Heretofore  the  methods  employed  in  the  study  of  the  hy- 
dration  of  metaphosphoric  acid  have  been  mostly  indirect,  and 
the  acid  used  was  prepared  either  by  dissolving  phosphorus 
pentoxide  in  cold  water  or  by  dehydrating  orthophosphoric  acid 
or  by  preparing  a  heavy  metal  salt  from  which  a  solution  of  the 
meta  acid  was  obtained  upon  the  withdrawal  of  the  metal  by 
hydrogen  sulphide.  Acidimetry  was  used  by  Sabatier1,  Monte- 
martinie  and  Egid2,  Bertholet  and  Andre3,  and  BalarefP ;  ther- 
mochemistry by  Giran5;  gravimetric  analysis  by  Holt  and 
Meyers6 ;  change  of  index  of  refraction  by  Blake  and  Blake7 ; 
change  of  conductivity  by  Prideaux8 ;  and  change  of  the  lower- 
ing of  the  freezing  point  by  Holt  and  Meyers9. 

In  their  gravimetric  method  Holt  and  Meyers  precipitated 
the  unchanged  metaphosphate  in  the  presence  of  ortho  and 
pyro  as  a  barium  metaphosphate  bearing  the  empirical  formula 
Ba(PO3)2.  By  repeated  experiments  with  mixtures  of  ortho, 
pyro,  and  meta  they  claim  very  little  variation  in  the  composi- 
tion of  their  precipitate.  However,  the  result  they  obtain  in 
the  measure  of  the  actual  hydration  is  the  best  criterion  of  the 
trustworthiness  of  their  method.  Judging  from  the  irregu- 
larity of  the  curve  they  publish  it  seems  that  their  method  is 
open  to  question  or  fraught  with  a  considerable  error. 

Other  attempts  to  apply  methods,  of  precipitation  were 
employed  to  show  whether  or  not  pyrophosphoric  acid  was 
formed  during  the  process  of  hydration10.  Neither  method 
is  applicable  to  the  problem.  Because  on  the  one  hand, 
the  method  of  Bertholet  and  Andre  requires  the  heating 
of  the  solution  to  be  analysed  acidified  with  acetic  acid 
on  a  boiling  water  bath  for  three  or  four  hours  to  secure 
the  formation  of  an  uncertain  magnesium  ammonium  pyro- 


1  Compt  rendu  106,  63  (1888),  108,  734  and  804  (1889). 

2  Gazz.  Ital.  Chim.  31, 1,  394  (1901). 

3  Compt.  rendu  124,  261  (1897). 

*  Zeit.  Anog.  Chem.  72,  85  (1911). 
3  Compt.  rendu  135,  1333  (1902). 
6J.  S.  C.  Trans.  99,  384  (1911). 
7  Am.  Chem.  J.  27,68(1902). 
s -Chem.  News  99,  161!  (1909). 

9  J.  C.  S.  Trans.  99,  385  (1911),  103,  532  (1913). 

10  Balareff,  Zeit.  Anorg.  Chem.  68,  266  (1910). 

Bertholet  and  Andre,  Compt.  rendu.  124,  261  (1897). 

8 


phosphate,  —  a  treatment  entirely  out  of  the  question  in 
view  of  the  marked  effects  of  temperature  and  hydrogen  ion 
upon  the  rate  of  hydration.  On  the  other  hand  the  precipita- 
tion of  pyrophosphate  of  copper  or  cadmium  in  an  acetic  acid 
solution,  the  method  employed  by  Balareff,  is  open  to  question 
because  upon  it  he  based  his  contention  that  no  pyrophosphate 
as  an  intermediate  product  was  formed  during  the  hydration, — 
a  statement  not  in  harmony  with  his  later  work1. 

There  have  been  two  different  opinions  as  to  whether  pyro- 
phosphoric  acid  was  formed  as  an  intermediate  product  during 
the  hydration  of  metaphosphoric  acid  to  ortho.  One  group 
of  chemists  maintained  that  the  hydration  was  direct  to  ortho, 
while  another  claimed  pyrophosphoric  acid  as  an  intermediate 
product.  The  former  was  supported  by  Graham2,  Sabatier3, 
Montemartini  and  Egid4,  and  Balareff5;  while  Bertholet  and 
Andre6,  Giran7,  Holt  and  Meyers8,  and  Balareff9  adhered  to  the 
latter. 

Accordingly  a  method  has  been  devised  and  materials  pre- 
pared for  the  attack  of  this  problem  whereby  the  conditions  and 
factors  influencing  the  reaction  may  be  studied  to  a  better  ad- 
vantage by  direct  standard  analytical  methods.  An  account  of 
the  investigation  will  be  presented  under  the  following  head- 
ings :  Apparatus,  Preparation  of  Materials,  Method  of  Pro- 
cedure, Experimental  Data,  Discussion,  and  Summary. 


1  Zeit.  Anorg.  Chem.  96,  103  (1916). 

2  Phil.  Trans.  123,  53  (1833). 
3Compt.  rendu.  106,  63  (1888). 

4  Gazz.  Ital.  Chim.  31,  I,  394  (1901). 

5  Zeit.  Anorg.  Chem.  67,  234  (1909)  ;  68,  288  (1910). 

6  Compt.  rendu.  123,  776  (1896)  ;  124,  265  (1897). 

7  J.  Russ.  Chem.  Soc.  30,  99. 
8J.  C.  S.Trans.  99,385  (1911). 

9  Zeit.  Anorg.  Chem.  96,  103  (1916). 


APPARATUS. 


Thermostat.  A  Freas  sensitive  thermostat  was  used  to 
maintain  a  constant  temperature  for  the  entire  work  of  hydra- 
tion  and  hydrogen  ion  concentration  measurement.  By  it  a 
constant  temperature  of  45°  C.  ±  .005  was  secured. 

Potentiometer.  Measurements  for  the  determination  of 
the  concentration  of  hydrogen  ion  were  made  with  a  Leeds  and 
Northrup  direct  reading  potentiometer  of  low  resistance. 

Galvanometer.  In  connection  with  the  potentiometer,  a 
Leeds  and  Northrup  type  R,  D'Arsonval  galvanometer  equip- 
ped with  a  telescope  and  scale  was  employed.  Its  resistance 
was  550  ohms,  its  sensibility  2000  megohms  (5  X  10~10  amp. 
per  mm.  at  one  meter).  The  period  was  six  seconds,  and  the 
critical  damping  resistance  11,500  ohms. 

Standard  Cell.  A  model  4  No.  3921  Weston  standard  cell 
served  as  a  basis  for  all  electrical  measurements.  Its  value 
was  1.01889  volts.  This  voltage  was  checked  against  a  cell 
whose  value  was  checked  against  a  Bureau  of  Standards 
standard. 

Calomel  and  Hydrogen  Cells  and  Electrodes.  The  calo- 
mel and  hydrogen  cells  and  electrodes  employed  in  the  meas- 
urement of  hydrogen  ion  concentration  were  of  the  type  de- 
scribed in  the  article  of  Fales  and  Vosburg1,  excepting  a  modi- 
fication of  the  hydrogen  cell  by  a  stopcock  on  the  arm  leading 
to  the  salt  bridge. 

Crucible  Furnace.  All  the  sodium  monometaphosphate 
was  prepared  in  an  electric  resistance  furnace.  It  was  cali- 
brated for  temperature  by  a  thermocouple  in  such  a  way  that 
its  temperature  could  be  controlled  by  measurement  of  the 
current. 


.  A.  C.  S.  40,  1291  (1918). 

10 


PREPARATION  OF  MATERIALS. 


MONO-SODIUM  PHOSPHATE— NaH2PO4    2H2O 

A  quantity  of  the  purest  mono-sodium  phosphate  obtain- 
able was  recrystallized  three  times  from  distilled  water.  The 
precipitation  was  accomplished  each  time  by  adding  to  the 
aqueous  solution  an  equal  volume  of  redistilled  95%  alcohol 
and  cooling  in  ice  water.  The  solution  was  constantly  stirred 
till  the  precipitation  was  complete.  In  this  way  a  very  uniform 
crystalline  product  was  obtained.  Upon  the  addition  of  the 
alcohol  two  liquid  phases  were  formed.  As  the  solid  phase  ap- 
peared the  upper  liquid  phase  gradually  disappeared  till  there 
was  but  one  liquid  and  one  solid  phase  at  complete  precipita- 
tion. Crystals  appeared  first  at  the  juncture  of  the  two  liquid 
phases.  Attempts  to  dry  the  hydrate  both  by  placing  it  in  a 
desiccator  over  fused  calcium  chloride  and  in  an  oven  at  40°  C. 
proved  fruitless.  Subsequent  analyses  for  water  of  hydration 
from  crystals  dried  in  this  way  gave  widely  varying  results. 
Hence  the  drying  had  to  be  accomplished  in  another  manner. 

The  crystals  already  wet  with  water  and  alcohol  were 
washed  three  times  with  redistilled  alcohol  on  a  Buchner  fun- 
nel with  suction.  Then  the  washing  was  continued  three  times 
with  redistilled  anhydrous  ether.  The  filter  was  changed  after 
each  ether  washing  to  avoid  the  retention  of  water  and  alcohol 
by  the  filter  paper.  The  hydrate  was  then  spread  out  upon  a 
clean  surface  and  stirred  to  allow  the  ether  to  evaporate.  A 
day  for  the  final  drying  was  selected  when  the  humidity  was 
low.  Otherwise  the  ^evaporation  of  the  ether  would  cause  a 
condensation  of  the  moisture  in  the  air  upon  the  surface  of  the 
crystals.  About  fifteen  minutes  at  20°  to  25°  C.  completed  the 
drying.  The  hydrate  was  then  kept  in  a  tightly  stoppered 
bottle.  Analyses  were  made  on  two  different  lots,  one  prepared 
and  analysed  in  March,  the  other  in  September  with  results  as 
follows : 

Water  of  hydration  plus 
Lot  Sample  water  of  constitution 

1  1  34.47% 

1  2  34.52% 

2  1  34.73% 


The  theoretical  for  the  hydrate  NaH2PO4-2H20  is  34.63%.  The 
above  figures  were  obtained  by  transforming  the  orthophos- 
phate  to  the  meta  according  to  the  method  outlined  below  for 
the  preparation  of  sodium  monometaphosphate. 

SODIUM  MONOMETAPHOSPHATE— NaPO3. 

Sodium  monometaphosphate  was  prepared  by  dehydrating 
the  NaH2PO4-2H2O  as  above  prepared  in  the  electric  furnace 
formerly  described  in  the  following  manner:  The  hydrate  in 
a  large  platinum  crucible  was  held  at  a  temperature  of  200°  C. 
for  an  hour.  The  temperature  was  then  slowly  raised  during 
the  next  hour  till  the  mass  melted  to  a  clear  liquid.  It  was  held 
at  this  temperature — approximately  600°  C. — for  ten  minutes. 
The  rheostat  was  set  finally  so  that  a  temperature  of  450°  C. 
was  maintained  for  the  next  two  hours  while  the  substance 
crystallized.  At  the  end  of  this  crystallization  the  metaphos- 
phate  was  quickly  cooled  by  dipping  the  bottom  of  the  crucible 
in  cold  water.  About  thirty-five  grams  could  be  prepared  at 
one  time  in  this  way. 

The  sodium  metaphosphate  above  prepared  was  investi- 
gated by  the  freezing  point  method  with  the  following  results  : 

Sodium  meta-  Water  in  Freezing  Molecular 

phosphate  in  grams  grams          point  depression  weight 

5.0472  100  .916°  102.5 

2.8159  100  .546°  95.9 

1.3435  100  .351°  86.9 

These  depressions  indicate  a  sodium  metaphosphate  whose 
molecular  weight  corresponds  to  the  formula  NaPo3  (Theoreti- 
cal— 102.04).  The  above  sodium  monometaphosphate  was  for- 
merly prepared  in  a  somewhat  similar  way1  from  sodium  am- 
monium hydrogen  phosphate  by  heating  the  resulting  vitrious 
mass  from  fusion  till  it  crystallized  or  by  slow  cooling  from 
fusion.  By  taking  2.77  grams  of  their  crystals  in  100  c.  c.  of 
water,  Holt  and  Meyers  obtain  a  depression  of  .51°  which  cor- 
responds to  a  molecular  weight  of  102  and  a  formula  of  NaPO3 . 


1  Tantatar,  J.  Russ.  Phys.  Chem.  Soc.,  30,  99 ;  Holt  and  Meyers,  J.  C.  S. 
Trans.  103,  535. 

12 


An  optical  study  of  the  sodium  monometaphosphate  made 
by  Mr.  R.  J.  Colony  of  the  Department  of  Geology  of  Columbia 
University  confirms  our  belief  that  the  sodium  monometaphos- 
phate prepared  above  is  a  distinct  chemical  individual.  Through 
the  kindness  of  Mr.  Colony  we  are  permitted  to  publish  the  fol- 
lowing optical  properties :  It  has  an  index  of  refraction, 
Ng=  1.486  ±  .005,  -Np  =  1.473  ±  .005,  birefringence  Ng— Np 
—  .013  ±  .005.  It  is  apparently  monoclinic,  optically  negative 
and  biaxial  with  a  large  optical  angle.  It  shows  uniformity  in 
behavior,  form,  and  composition. 

Sodium  monometaphosphate  is  very  soluble  in  water.  It 
reacts  acid  to  litmus,  a  three-tenths  molar  aqueous  solution 
gives  a  hydrogen  ion  concentration  of  6.5  x  10~7  moles  per  liter. 
From  a  three-tenth  molar  solution  white  flocculent  precipitates 
which  change  to  crystalline  form  on  standing,  may  be  obtained 
from  solutions  of  the  nitrates  of  silver,  lead,  mercury,  and  bis- 
muth. With  solutions  of  the  nitrates  of  zinc,  cadmium,  cobalt, 
nickel,  and  copper,  white  amorphous  precipitates  are  formed. 
It  does  not  give  a  precipitate  in  a  solution  containing  mag- 
nesium chloride,  ammonius  chloride,  and  ammonium  hydroxide 
in  moderately  high  concentrations,  the  property  employed  in 
the  separation  of  monometaphosphoric  acid  from  orthophos- 
phoric  acid. 

HYDROCHLORIC  ACID. 

The  hydrochloric  acid  used  was  prepared  by  distilling  a 
constant  boiling  solution  through  a  quartz  condenser.  The  first 
and  last  portions  were  rejected. 

POTASSIUM  CHLORIDE. 

The  calomel  cells  and  salt  bridges;  -were  prepared  from 
potassium  chloride  which  was  purified  by  recrystallization  three 
times  from  distilled  water  and  fusion  in  platinum. 

MERCUROUS  CHLORIDE. 

The  mercurous  chloride  employed  to  make  calomel  cells 
for  hydrogen  ion  measurement  was  prepared  by  the  electrolytic 
method  of  Ellis1  from  mercury  redistilled  according  to  Hulett 
and  hydrochloric  acid  prepared  as  described  above. 


.  A.  C.  S.  38,737  (1916). 

13 


MAGNESIA  MIXTURE. 

The  magnesia  mixture  used  was  prepared  by  dissolving 
137.5  grams  of  magnesium  chloride,  225  grams  of  ammonium 
chloride,  and  250  c.  c.  ammonium  hydroxide  (specific  gravity 
.9)  in  2250  c.  c.  of  water. 


METHOD  OF  PROCEDURE. 


In  planning  a  method  of  procedure  the  factors  influencing 
the  reaction  have  as  far  as  possible  been  either  measured  or 
controlled.  The  temperature,  the  concentration  of  sodium 
monometaphosphate,  the  concentration  of  orthophosphate,  the 
formation  of  pyrophosphate,  and  the  concentration  of  hydro- 
gen ion  are  the  variable  factors  which  influence  the  hydration 
of  sodium  monometaphosphate. 

The  temperature  was  regulated  and  controlled  at  45°  C.  — 
.005°.  The  metaphosphoric  acid  was  separated  from  the  ortho 
and  the  amount  of  the  latter  determined  directly.  By  differ- 
ence the  unchanged  meta  was  obtained.  No  satisfactory  quan- 
titative method  has  as  yet  been  found  whereby  pyrophosphoric 
acid  may  be  determined  in  mixtures  such  as  occur  in  this  inves- 
tigation. So,  by  other  means,  an  estimate  of  the  amount  formed 
is  all  that  is  possible.  The  concentration  of  hydrogen  ion  was 
measured  at  intervals  during  the  hydration. 

PREPARATION  OF  SOLUTIONS. 

All  solutions  made  up  for  hydration  were  prepared  at 
20°  C.  The  carefully  dried  and  finely  pulverized  sodium  mono- 
metaphosphate was  weighed  and  introduced  into  a  volumetric 
flask.  Distilled  water  was  added  and  the  salt  completely  dis- 
solved. One-half  hour  was  usually  required  for  complete  solu- 
tion at  room  temperature.  The  volume  was  increased  till  suffi- 
cient room  was  left  for  the  introduction  of  the  required  amount 
of  hydrochloric  acid  used  to  furnish  the  hydrogen  ion  concen- 
tration in  the  particular  solution.  The  acid  was  the  constant 
boiling  mixture  previously  described  whose  value  had  been 
determined  by  measuring  out  30  c.  c.  portions  by  means  of  a 
burette  and  building  them  up  to  1000  c.  c.  The  final  acid  solu- 
tions were  titrated  with  a  standard  sodium  hydroxide  solution 
whose  value  was  gotten  by  using  Bureau  of  Standards  benzoic 
acid.  Phenolphthalein  was  used  as  an  indicator.  As  the  acid 
was  added  the  flask  was  rotated  so  as  to  keep  from  acquiring 
as  little  as  possible  a  higher  concentration  of  hydrogen  ion  in 

15 


any  portion  of  the  solution  than  that  ultimately  desired.  After 
the  introduction  of  the  acid  the  solution  was  quickly  cooled  to 
20°  C.  and  the  flask  rilled  up  to  the  graduation.  After  thorough 
mixing,  the  solution  was  put  in  a  "non-sol"  bottle  and  placed 
in  the  bath.  The  whole  operation,  beginning  with  the  addition 
ot  the  acid,  required  not  more  than  ten  minutes. 

The  specific  gravity  of  the  solution  was  taken  at  20°  C.  by 
means  of  a  Westphal  balance  at  the  beginning  of  the  reaction. 
No  change  of  volume  was  observed  during  the  hydration  great- 
er than  one  part  in  one  thousand,  the  precision  of  the  bal- 
ance1 .  Hence  one  specific  gravity  measurement  for  each  solu- 
tion served  as  a  basis  for  calculation  of  the  percentage  of  meta- 
phosphoric  acid  transformed  to  the  ortho.  The  concentrations 
of  the  solutions  were  all  calculated  in  moles  per  liter.  There- 
fore, knowing  the  specific  gravity  and  the  concentration  in 
moles  per  liter,  the  amount  of  sodium  monometaphosphate  in 
any  weighed  quantity  of  solution  could  be  determined. 

THE  SEPARATION  OF  MONOMETAPHOSPHORIC  ACID  FROM 
ORTHOPHOSPHORIC  ACID. 

Monometaphosphoric  acid  was  separated  from  orthophos- 
phoric  acid  by  means  of  magnesia  mixture  in  a  cold  solution. 
As  previously  stated,  a  solution  of  sodium  monometaphosphate 
does  not  give  a  precipitate  with  magnesia  mixture  in  concen- 
trations used  in  this  procedure  and  in  fact  very  much  higher 
concentrations.  This  method  of  separation  has  been  tested  both 
qualitatively  and  quantitatively  (see  Table  1).  Seven-tenths 
of  a  gram  of  sodium  monometaphosphate  together  with  25  c.  c. 
of  the  magnesia  mixture  prepared  above  in  a  total  volume  of 
125  c.  c.  was  allowed  to  stand  twenty-four  hours  repeatedly  and 
no  precipitate  appeared  while  a  precipitate  of  the  orthophos- 
phate  appeared  immediately  in  another  solution  similarly 
treated,  excepting  that  one  milligram  of  phosphorus  in  the 
form  of  orthophosphate  was  added.  It  remains  now  to  be 
shown  that  monometaphosphoric  acid  is  quantitatively  separ- 
able from  the  ortho  and  that  no  appreciable  hydration  occurs 
during  the  time  of  standing  required  for  the  precipitation  of 


1  Montemartini  and  Egid,  Gazz.  Ital.  Chim.  31,  I,  394  (1901). 

16 


12 

C    PL, 


W)  O 

6^ 


PH^ 
GO   eo 

., 


ig^ 

e  PH 


* 


fr- 


i§a 

W^2 


i-H   CO  CVJ 

QN  ON  ON 


fO  PO  CO 
co  ro  co 


00  ON 

ig 


re  PO  ro 
ro  <^  fO 
ON  ON  ON 


Srx  O 
.  ^  ^ 

10  10  10 


ro  fO  CO 
ro  ro  CO 

ON  ON  ON 


CO  ro 


CO  ro  I-H  rh 


I-H  CM  10 

O^T-H 


ro  fO  ro 
ro  ro  ro 
ON  ON  ON 


17 


the  magnesium  ammonium  phosphate.  By  referring  to  Table 
1  it  may  be  noted  that  thirty  determinations  of  orthophosphate, 
according  to  the  method  outlined  below,  in  the  presence  of 
varying  quantities  of  sodium  monometaphosphate  from  900 
milligrams  to  100  milligrams  have  been  made.  The  amount  of 
orthophosphate  used  has  varied  and  the  time  of  standing  has 
been  6,  12,  and  18  hours  respectively.  There  is  an  increase  in 
amount  found  over  the  amount  added  which  is  of  the  same 
order  irrespective  of  the  time  of  standing,  whether  it  was  6,  12, 
or  18  hours.  This  shows  that  hydration  is  not  the  cause  of  the 
increase;  for  if  it  were,  the  amount  of  increase  would  be  a 
direct  function  of  the  time.  The  increase  seems  to  be  due  to 
absorption  of  the  sodium  monometaphosphate  by  the  mag- 
nesium ammonium  phosphate  precipitate,  which  is  subsequent- 
ly hydrated  during  the  dissolving  of  the  magnesium  ammonium 
phosphate  with  hot  hydrochloric  acid.  The  reaction  as  will  be 
shown  is  rapid  in  a  hot  acid  solution. 

The  analyses  were  run  in  series  of  five  each  and  the  time 
of  standing  in  the  hot  acid  solution  was  about  the  same  for  all 
except  the  one  starred  in  Table  1.  This  one  was  re-precipitated 
immediately  and  the  value  of  it  is  smaller  than  that  obtained 
for  both  the  one  that  stood  six  and  the  one  that  stood  18  hours 
in  the  presence  of  the  same  amount  of  sodium  monometaphos- 
phate. At  any  rate  the  maximum  deviation  from  the  amount 
used  is  not  greater  than  .82  of  a  milligram  of  phosphorus  or 
1.5%.  From  the  experimental  data  below  it  will  be  observed 
that  almost  all  the  determinations  were  made  in  the  presence 
of  much  less  than  300  milligrams  of  sodium  monometaphos- 
phate where  the  maximum  deviation  is  in  the  region  of  .5  milli- 
gram or  one  per  cent. 

DETERMINATION  OF  ORTHOPHOSPHATE, 

Orthophosphate  was  determined  by  the  standard  gravi- 
metric method.  The  samples  of  the  solution  were  taken  by 
means  of  Bailey  weighing  burettes.  A  standard  final  volume 
of  125  c.  c.  including  25  c.  c.  of  magnesia  mixture  was  used  in 
all  determinations.  Before  precipitation  each  sample  was  di- 
luted to  100  c.  c.  The  separation  of  the  magnesium  ammonium 

18 


phosphate  precipitate  from  the  unprecipitated  meta  was  made 
by  filtration  not  longer  than  sixteen  hours  nor  less  than  six 
hours  after  the  first  precipitation.  After  separation  and  wash- 
ing with  an  ammonium  hydroxide-ammonium  nitrate  solution, 
the  orthophosphate  precipitate  was  dissolved  with  hot  hydro- 
chloric acid,  re-precipitated  by  adding  to  the  solution  diluted 
to  100  c.  c.  a  concentrated  ammonium  hydroxide  solution  (sp. 
gr.  .9),  10  c.  c.  in  excess  of  that  required  for  neutralization. 
Finally  after  twelve  hours  standing  the  magnesium  ammonium 
phosphate  was  filtered  through  a  weighed  gooch  crucible,  wash- 
ed, and  ignited  and  weighed  as  magnesium  pyrophosphate. 
By  this  method  the  amount  of  the  monometaphosphate  trans- 
formed to  ortho  could  be  determined. 

FORMATION  OF  PYROPHOSPHATE. 

The  analytical  results  vary  somewhat  due  to  the  forma- 
tion of  pyrophosphate  in  the  reaction.  With  no  method  at  pres- 
ent for  the  separation  of  pyrophosphoric  acid  from  the  ortho 
except  the  prevention  of  its  precipitation  by  an  excess  of  mag- 
nesia mixture  (magnesium  pyrophosphate  is  soluble  in  an  ex- 
cess of  magnesium  salts)  at  times  the  ortho  precipitate  was  con- 
taminated a  little  with  it.  That  there  was  pyrophosphoric  acid 
formed  there  was  no  doubt.  The  magnesium  ammonium  phos- 
phate is  a  definite  crystalline  product  very  readily  filtered. 
When  pyrophosphate  is  present  these  crystals  are  mixed  with 
a  white  gelatinous  precipitate  which  is  soluble  in  an  excess  of 
magnesium  salts.  The  formation  of  pyrophosphate  was  later 
confirmed  by  hydrogen  ion  measurements. 

MEASUREMENT  OF  CONCENTRATION  OF  HYDROGEN  ION. 

All  hydrogen  ion  measurements  were  made  at  45°  C.  by 
The  Saturated  Potassium  Chloride  'Calomel  Cell  method  de- 
veloped in  this  department1.  Samples  of  the  solution  in  process 
of  hydration  were  taken  by  means  of  a  pipette  and  introduced 
into  the  hydrogen  cell  previously  steamed  and  rinsed  three 
times  with  the  solution  being  measured.  After  fifteen  minutes 


1  Kales  -and  Mudge,  J.  A.  C.  S.  42,  2434  (1920). 

19 


the  time  required  for  the  system  to  reach  equilibrium,  the  meas- 
urement was  made.  The  hydrogen  used  was  purified  by  pass- 
ing it  successively  through  acid  permanganate,  alkaline  pyro- 
gallol,  and  a  portion  of  the  same  solution  to  be  measured  placed 
in  the  thermostat. 

The  calculations  for  the  molar  concentration  of  hydrogen 
ion  were  made  by  means  of  the  formula, 

A  —  E 


derived  from  the  Nernst  formula. 

In  this  formula  C  is  the  concentration  of  the  hydrogen  ion 
in  moles  per  liter,  T  the  absolute  temperature,  B  a  constant 
whose  value  is  .000198  obtained  in  the  transformation  of  R  in 

RT         C± 
the    formula    used,    E  =  -  In  -    to    volt-coulombs    and 

nF         C, 

subsequently  dividing  by  96,494  coulombs  multiplied  by  the 
equivalence  of  hydrogen  and  the  logarithmic  modulus  .4343 
thus  fixing  its  dimensions  as  volts  ;  E,  the  observed  voltage, 
and  A  a  constant  determined  experimentally  by  measurement 
of  a  .0989  M.  hydrochloric  acid  solution  whose  value  was  prev- 
iously checked  against  Bureau  of  Standards  Benzoic  acid.  By 
employing  the  precentage  91.3%,  for  a  .1  M  hydrochloric  acid 
solution  determined  from  the  data  and  curves  in  the  Carnegie 
Publications  for  1907  by  Noyes  and  others,  pages  141  and  339, 
a  value  of  .2356  is  obtained  whose  dimensions  are  also  volts  — 
the  theoretical  voltage  of  a  one  molar  hydrogen  ion  solution 
for  the  combination  used  in  this  research.  The  difference  in 
ionization  between  a  .0989  M.  and  a  .1  M.  hydrochloric  acid 
solution  is  less  than  the  experimental  error.  The  formula  for 
45°  C.  becomes 

.2356  —  E  .2356  —  E 

log  CH<  -  - 

.000198  (45  +  273)  .063 


20 


EXPERIMENTAL  DATA. 


The  following  table  outlines  the  plan  adopted  in  securing 
experimental  data  on  hydration  of  solutions  of  different  hy- 
drogen ion  and  monometaphosphate  concentrations. 


TABLE  2. 

Solutions  studied. 

Solution 

Cone.  NaPO3 
moles  per  liter 
at  20°  C. 

Cone.  HC1 
moles  per  liter 
at  20°  C. 

Specific  gravity 
at  20°  C. 

c 

.5 

.483 

1.045 

D 

.5 

.483 

1.044 

G 

.5 

.339 

1.041 

E 

.5 

.339 

1.042 

B 

.5 

.192 

1.042 

H 

.5 

.192 

1.041 

K 

.3 

.339 

1.025 

M 

.3 

.339 

1.026 

N 

.1 

.339 

1.011 

O 

.1 

.339 

1.011 

Z 

.3 

.010 

1.025 

ZA 

.3 

.010 

1.025 

s 

.3 

.000 

1.025 

SA 

.3 

.000 

1.025 

From  the  outline  it  will  be  observed  that  hydrations  were 
run  in  duplicate  with  the  exception  of  the  last  four.  Duplicate 
samples  of  the  latter  were  taken  as  shown  by  tables  which 
follow. 

The  hydration  and  hydrogen  ion  concentration  tables  of 
solutions  C,  G,  B,  M,  and  N  which  are  duplicates  of  D,  E,  H, 
K,  and  O  respectively  have  been  omitted.  The  mean  deviation 
of  the  results  in  duplicates  is  not  greater  than  five  per  cent 
when  the  concentration  of  pyrophosphate  is  high  at  the  begin- 
ning nor  greater  than  one  per  cent,  when  the  hydration  nears 
completion. 

21 


TABLE  3. 
Hydration  in  Solution  D. 

Concentration  NaPO3  =  —  5  M.  at  20°  C. 
Temperature  =  45°  C. 
Concentration  HC1  =  .483  M.  at  20°  C. 
Specific  Gravity  =  1.044  at  20°  C. 


No.  of 

Time 

Total  Phos- 

Phosphorus as 

Percentage 

sample 

hrs.  min. 

phorus  in  rugs. 

ortho  in  nigs. 

hydrated 

1 

1:45 

89.61 

7.41 

8.27 

2 

4:40 

79.14 

37.32 

47.13 

3 

10:40 

78.30 

51.71 

65.99 

4 

24:10 

79.37 

64.81 

81.59 

5 

48:25 

78.60 

69.15 

87.93 

6 

72:55 

79.84 

74.20 

92.66 

7 

120:10 

78.89 

76.37 

96.74 

8 

168:42 

74.42 

73.31 

98.44 

9 

252:10 

78.15 

79.16 

101.20 

This  table  furnishes  the  data  for  the  curve  in  figure  1. 


TABLE  4. 
Hydrogen  Ion  Concentration  during  Hydration  in  Solution  D. 


No.  of 
sample 

1 
2 
3 
4 
5 
6 
7 
8 
9 
10 


Time 
hrs.  min. 

1:00 

5:15 

11:30 

25:15 

49:00 

74:25 

121 :25 

170:00 

243:00 

152:00 


Voltage 
.2667 
.2793 
.2838 
.2874 
.2924 
.2957 
.2977 
.3022 
.2995 
.2995 


Concentration  in 
moles  per  liter 

.3209 
.2024 
.1717 
.1506 
.1255 
.1112 
.1033 
.0877 
.0968 
.0968 


This  table  furnishes  the  data  for  the  curve  in  figure  1. 

22 


TABLE  5. 
Hydration  in  Solution  E. 

Concentration  of  NaPO3  =  .5  M.  at  20°  C. 
Temperature  =  45°  C. 
Concentration  of  HC1  =  .339  M.  at  20°  C. 
Sp.  Gr.  =  1.042  at  20°  C. 


No.  of 

Time 

Total  Phos- 

Phosphorus as 

Percentage 

sample 

hrs.  min. 

phorus  in  mgs. 

ortho  in  mgs. 

hydrated 

1 

2:10 

151.09 

11.43 

7.56 

2 

5:10 

77.36 

19.96 

25.80 

3 

11:10 

77.42 

38.91 

50.26 

4 

23:10 

76.37 

51.48 

67.41 

5 

48:35 

78.02 

58.59 

75.10 

6 

71:25 

80.03 

65.95 

80.53 

7 

119:03 

78.42 

66.09 

84.28 

8 

166:59 

72.98 

66.45 

91.05 

9 

239:25 

77.14 

73.84 

95.72 

10 

383  :25 

86.54 

87.16 

102.80 

This  table  furnishes  the  data  for  the  curve  in  figure  1. 


TABLE  6. 
Hydrogen  Ion  Concentration  during  Hydration  in  Solution  E. 


No.  of 
sample 

1 
2 
3 
4 
5 
6 
7 
8 
9 
10 


Time 
hrs.  min. 

1:35 

5:45 

10:55 

24:10 

47:20 

72:55 

120:10 

167:45 

240:40 

384:25 


Voltage 
.2823 
.2950 
.3004 
.3082 
.3138 
.3174 
.3216 
.3242 
.3276 
.3276 


Concentration  in 
moles  per  liter 

.1815 
.1140 
.0936 
.0704 
.0574 
.0503 
.0434 
.0392 
.0347 
.0347 


This  table  furnishes  the  data  for  the  curve  in  figure  1. 

23 


TABLE   7. 
Hydration  in  Solution  H. 

Concentration  of  NaPO3  =  .5  M.  at  20°  C. 
Temperature  =  45°  C. 
•Concentration  of  HC1  =  .192  M.  at  20°  C. 
Sp.  Gr.  =  1.041  at  20°  C. 


No.  of 
sample 

1 

2 

3 

4 

5 

6 

7 

8 
11 
12 
13 
14 
15 
16 
17 
18 


Time           Total  Phos- 
hrs.  min.    phorus  in  mgs. 
6:12          157.33 

Phosphorus  as       Percentage 
ortho  in  mgs.          hydrated 
21.74                  13.82 

13:22 

78.80 

23.22 

29.47 

23:29 

77.28 

34.70 

44.91 

35:57 
47:17 

84.62 
83.33 

Sample  lost  in 
52.82 

filtration 
63.38 

71:12 

81.57 

56.42 

69.16 

119:19 

59.59 

59.59 

73.40 

167:36 

75.55 

60.88 

80.58 

192:32 

77.12 

60.23 

78.11 

215:18 

79.55 

65.42 

82.42 

263  :42 

78.28 

66.65 

85.13 

335  :42 

79.63 

68.29 

85.76 

457:07 

85.64 

79.08 

92.34 

678:36 

79.46 

76.29 

96.01 

875:18 

67.23 

66.17 

98.43 

875:18 

94.86 

93.29 

98.36 

This  table  furnishes  the  data  for  the  curve  in  figure  1. 

TABLE  8. 
Hydrogen  Ion  Concentration  during  Hydration  in  Solution  H. 


No.  of 
sample 

1 

2 

3 
4 
5 
6 

7 
8 


Time 

hrs.  min. 

1:17 

5:55 

13:30 

24:30 

36:30 

48:15 

71:57 

120:25 


Voltage 
.2960 
.3147 
.3220 
33.13 
.3361 
.3386 
.3424 
.3487 


Concentration  in 

moles  per  liter 

.1101 

.0555 
.0425 
.0303 
.0254 
.0231 
.0202 
.0160 


24 


9 
10 
11 
12 
13 
14 
15 
16 


TABLE  8— Continued. 

168:17  .3522 

193 :25  .3533 

216:04  .3539 

264:34  .3563 

337 :00  .3580 

457:48  .3590 

673:10  .3614 

876:12  .3630 


.0141 
.0135 
.0133 
.0121 
.0114 
.0110 
.0100 
.0095 


This  table  furnishes  the  data  for  the  curve  in  figure  1. 

TABLE   9. 
Hydration  in  Solution  K. 

Concentration  of  NaPO3  =  .3  M.  at  20°  C. 
Temperature  =  45°  C. 
Concentration  of  HC1  =  .339  M.  at  20°  C. 
Sp.  Gr.  =  1.025  at  20°  C. 


No.  of 
sample 

1 

2 

3 

4 

5 

6 

7 

8 

9 
10 


Time 
hrs.  min. 

1:30 

Total  Phos- 
phorus in  mgs. 
190.96 

Phosphorus  as 
ortho  in  mgs. 

17.64 

Percentage 
hydrated 
9.24 

3:00 

146.91 

53.08 

36.05 

7:00 

97.77 

57.50 

58.82 

15:00 

61.37 

40.00 

65.17 

27:00 

79.75 

58.65 

73.54 

51:00 

72.86 

62.83 

86.22 

83:25 

93.01 

87.33 

93.89 

120:10 

50.88 

49.00 

96.31 

168:25 

49.18 

47.91 

97.44 

240:01 

46.05 

45.41 

98.60 

This  data  furnishes  the  data  for  the  curve  in  figure  2. 

TABLE    10. 
Hydrogen  Ion  Concentration  during  Hydration  in  Solution  K. 


No.  of 
sample 

1 

2 

3 


Time 

hrs.  min. 

1:10 

3:10 

7:55 


Voltage 
.2781 
.2808 
.2858 


Concentration  in 

moles  per  liter 

.2115 

.1917 

.1597 


25 


TABLE  1O— Continued 


4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 


14:50 

24:31 

50:05 

83:55 

120:44 

169:00 

194:26 

242:00 

250:53 

335 :07 

365 :45 


.2884 
.2929 
.2953 
.2969 
.3012 
.2997 
.2992 
.2992 
.3018 
.3006 
.3007 


.1452 
.1232 
.1128 
.1064 
.0909 
.0961 
.0978 
.0978 
.0900 
.0930 
.0926 


This  data  furnishes  the  data  for  the  curve  in  figure  2. 


TABLE  11. 
Hydration  in  Solution  O. 

Concentration  of  NaPO3  =  .1  M.  at  20°  C. 
Temperature  =  45°  C. 
Concentration  of  HC1  =  .339  M.  at  20°  C. 
Sp.Gr.=  1.011  M.  at  20°  C. 


No.  of 
sample 

Time          Total  Phos- 
hrs.  min.    phorus  in  mgs. 

Phosphorus  as 
ortho  in  mgs. 

Percentage 
hydrated 

1 

1:30 

97.86 

11.33 

11.83 

2 

3:00 

61.70 

25.95 

42.06 

3 

7:10 

64.07 

44.26 

69.08 

4 

13:10 

63.53 

50.26 

79.10 

5 

24:10 

70.02 

61.85 

88.34 

6 

47:40 

61.67 

59.34 

96.22 

7 

72:10 

62.90 

61.63 

97.89 

This  table  furnishes  the  data  for  the  curve  in  figure  3. 


26 


TABLE  12. 
Hydrogen  Ion  Concentration  during  the  Hydration  in  Solution  O. 


No.  of 
sample 

1 

2 

3 
4 

5 
6 

7 


Time 

hrs.  min. 

1:00 

3:45 

7:15 

13:40 

24:50 

49:00 

72:53 


Voltage 
.2715 
.2714 
.2734 
.2732 
.2751 
.2764 
.2760 


Concentration  in 
moles  per  liter 
.2702 
.2702 
.2522 
.2530 
.2361 
.2251 
.2284 


This  table  furnishes  the  data  for  the  curve  in  figure  3. 

TABLE  13. 
Hydration  in  Solution  Z  and  Z  A. 

Concentration  of  NaPO3  =  .3  M.  at  20°  C. 
Temperature  =  45°  C. 
Concentration  of  HC1  =  .01  M.  at  20°  C. 
Sp.  Gr.  =  1.022  at  20°  C. 


No.  of 

Time 

Total  Phos-     Phosphorus  as 

Percentage 

sample 

hrs.  min. 

phorus  in  mgs. 

ortho  in  mgs. 

hydrated 

1-Z-A 

166:15 

190.36 

23.41 

12.30 

2-Z-A 

166:15 

196.32 

23.58 

12.01 

3-Z-A 

333:00 

165.99 

42.51 

25.34 

4-Z-A 

333:00 

191.81 

.... 

.... 

5-Z-A 

501:00 

148.31 

64.64 

43.60 

6-Z-A 

501:00 

139.51 

56.14 

40.30 

7-Z 

665:00 

92.31 

44.88 

48.61 

8-Z 

665:00 

98.34 

47.61 

48.41 

9-Z 

952:30 

87.05 

51.15 

58.75 

10-Z 

952  :30 

99.95 

57.53 

57.57 

11-Z 

1386:45 

89.21 

65.14 

73.02 

12-Z 

1386:45 

101.11 

73.61 

72.81 

13-Z 

2248:30 

94.% 

82.65 

87.03 

14-Z 

2248:30 

103.65 

88.72 

87.58 

15-Z 

2944:45 

75.06 

70.07 

93.35 

16-Z 

2944:45 

66.49 

61.93 

93.15 

17-Z 

3469:20 

79.87 

77.43 

96.95 

18-Z 

3469:20 

72.21 

70.73 

97.14 

This 

table  furnishes  the  data  for 

the  curve  in 

figure  4. 

27 


TABLE   14. 
Hydrogen  Ion  Concentration  during  the  Hydration  in  Z. 

No.  of                       Time  Concentration  in 

sample                    hrs.  min.                  Voltage  moles  per  liter 

1  0:40                   .3637  .009477 

2  7:45                   .3777  .005552 

3  19:45                    .3829  .004591 

4  44:00                   .3896  .003594 

5  72:20                   .3960  .002844 

6  120:20                   .4039  .002131 

7  167:41                    .4089  .001841 

8  480:03                    .4258  .000957 

9  953:38                    .4393  .000584 

10  1553:45                   .4455  .000466 

11  2946:03                    .4507  .000384 

12  3570:47                    .4524  .000362 

This  table  furnishes  the  data  for  the  curve  in  figure  4. 

TABLE  15. 
Hydration  in  Solution  S  and  S-A. 

Concentration  NaPO3  =  .3  M.  at  20°  C. 
Temperature  =  45°  C. 
Concentration  HC1  =  0. 
Sp.  Gr.  =  1.022  at  20°  C. 


No.  of 
sample 
1-S-A 

Time 
days 

25 

Total  Phos- 
phorus in  mgs. 
621.02 

Phosphorus  as 
ortho  in  mgs. 
11.21 

Percentage 
hydrated 
1.81 

2-S-A 

25 

593.65 

10.62 

1.79 

3-S-A 

45 

448.48 

23.80 

5.31 

4-S-A 

45 

443.94 

22.09 

5.00 

5-S 

60 

232.07 

17.31 

7.46 

6-S 

60 

240.47 

18.20 

7.56 

7-S 

74 

132.17 

13.77 

10.42 

8-S 

74 

152.78 

15.89 

10.40 

9-S 

88 

115.72 

15.22 

13.15 

10-S 

88 

118.56 

15.80 

13.33 

11-S 

109 

99.44 

19.54 

19.65 

12-S 

109 

90.76 

17.67 

19.47 

28 


TABLE  15— Continued. 


13-S 

149 

91.92 

29.80 

32.42 

14-S 

149 

99.52 

32.00 

32.23 

15-S 

177 

98.02 

40.56 

41.37 

16-S 

177 

98.13 

40.67 

41.44 

17-S 

200 

99.83 

47.91 

49.11 

18-S 

200 

99.21 

48.28 

49.16 

This  table  furnishes  the  data  for  the  curve  in  figure  5. 

TABLE  16. 
Hydrogen  Ion  Concentration  during  Hydration  in  Solution  S. 


No.  of 

Time 

Concentration  x  106 

sample 
1 

hrs.  min. 
1:30 

Voltage 

.6252 

in  moles  per  liter 
.65 

2 

4:30 

.6234 

.70 

3 

10:48 

.6195 

.81 

4 

23:00 

.6070 

1.27 

5 

48:30 

.5900 

2.37 

6 

72:00 

.5798 

3.44 

7 

96:00 

.5636 

6.22 

8 

199:15 

.5679 

5.31 

9 

216:50 

.5641 

6.11 

10 

289:43 

.5565 

8.06 

11 

343  :37 

.5555 

8.36 

12 

480:36 

.5449 

12.30 

13 

602:45 

.5406 

14.52 

14 

724:45 

.5373 

16.68 

15 

890:45 

.5339 

18.41 

16 

1158:40 

.5284 

22.51 

17 

1494:33 

.5248 

25.68 

18 

2183  :50 

.5209 

29.61 

19 

4799  :28 

.5109 

41.80 

This  table  furnishes  the  data  for  the  curve  in  figure  5. 

29 


TABLE  17. 

The  Concentration  of  Hydrogen  Ion  in  Monosodiumphosphate 
Hydrochloric  Acid  Solutions. 

(The  solutions  were  made  up  at  20°  C.  and  measured  at  45°  C.) 
Concentration  HC1  Moles  per  liter  at  20°  C. 


0 

.1 

.2 

Con. 

<W 

Js  . 

o 

voltage 

H+xlO* 

voltage 
.3013 

Con.  H" 
.0906 

voltage 
.2834 

Con.  H 

.1743 

Concentrat: 
NaH2P04  M 
per  Litei 

.1 
.2 
.3 
.4 

.5225 
.5172 
.5126 
.5085 

.2793 
.3390 
.4014 
.4659 

.3336 
.3624 
.3772 
.3874 

.0278 
.0097 
.0057 
.0039 

.2979 
.3190 
.3398 
.3537 

.1026 
.0474 
.0221 
.0133 

.5 

.5049 

.5313 

.3949 

.0039 

.3638 

.0092 

Concentration  HC1  Moles  per  liter  at  20°  C. 

.3                          .4  .5 

Con. 

„,               voltage     H+xlO4  voltage     Con.  H+  voltage  Con.  H 

1 1  u  0     .2719      .2653        .2630      .3674  .2595  .4176 

fajj  .1      .2790      .2047        .2683      .3027  .2599  .4114 

|g  *i  .2     .2932      .1241        .2774      .2170  .2670  .3162 

Isf&.S     .3105      .0647        .2889      .1426  .2753  .2343 

^£      .4     .3262      .0352        .3026      .0864  .2858  .1597 

.5     .3389      .0229        .3175      .0501  .2969  .1064 


The  data  in  this  table  serve  as  a  basis  for  plotting  curves 
in  figure  6. 


30 


TABLE   18. 

Concentration  of  Hydrogen  Ion  in  Sodium  Bi-pyrophosphate 
Hydrochloric  Acid  Solution. 

(The  solutions  were  made  at  23°  C.  and  measured  at  45°  C.) 
Concentration  HC1  Moles  per  liter. 

.192  .339  .483 

voltage      Con.  H"      voltage       Con.  H+      voltage    Con.  H+ 

§•§•    .01  .2820  .1834  .2656  .3340  .2562  .4710 

|*Jj«  .2910  .1320  .2722  .2625  .2595  .4175 

^cTS.10  .2981  .1019  .2755  .2326  .2624  .3755 

!£f|.15  .3055  .0777  .2791  .2039  .2655  .3353 

dj*    .20  .3130  .0591  .2822  .1821  .2680  .3060 

525      .25  .3197  .0462  .2880  .1473  .2695  .2898 

To  obtain  the  Na2H2P2O7,  the  normal  sodium  pyrophos- 
phate  was  used  and  additional  HC1  to  that  indicated  in  Table  18 
was  added  so  that  the  ratio  of  two  moles  of  HC1  to  one  mole  of 
Na4P2O7  was  maintained  in  each  solution  in  excess  of  that 
tabulated.  The  data  in  this  table  serve  as  a  basis  for  plotting 
curves  in  figure  8. 


31 


DISCUSSION 


CHANGE  OF  CONCENTRATIONS  OF  HYDROGEN  ION. 

A  comparison  of  the  data  from  the  various  solutions  stud- 
ied reveals  the  great  influence  hydrogen  ion  has  upon  the  hy- 
dration  of  sodium  monometaphosphate.  By  the  direct  method 
employed  it  was  possible  to  add  hydrogen  ion  and  determine 
its  influence.  The  experimental  data  in  the  tables  above  and 
the  curves  in  figures  1,  2,  3  and  4  show  how  the  hydrogen 
effects  the  rate  of  hydration  and  how  there  is  a  progressive 
decrease  of  hydrogen  ion  during  the  reaction.  This  decrease  is 
very  readily  explained  by  the  withdrawal  of  hydrogen  ion  by 
the  less  dissociated  ortho  and  pyrophosphoric  acids  formed  in 
the  reaction.  In  tables  17  and  18  and  curves  in  figures  6  and  8 
it  is  shown  that  there  is  a  gradual  lowering  of  the  hydrogen 
ion  concentration  by  increasing  both  the  ortho  and  pyrophos- 
phate  concentrations  separately.  In  all  solutions  studied  this 
decrease  of  hydrogen  ion  has  been  evident  except  in  solution  S 
tables  15  and  16  and  figure  5  where  there  was  an  actual  in- 
crease. This  change  in  the  hydrogen  ion  concentration  is  mark- 
edly pronounced  even  when  our  method  showed  very  little  or 
no  orthophosphate  in  solution  after  considerable  time.  This  is 
shown  in  curves  of  figures  1,  2,  3,  4  and  5. 

PERIOD  OF  APPARENT  INHIBITION. 

In  figures  1,  2,  3,  4  and  5  all  hydration  curves  show  periods 
of  apparent  inhibition.  In  hydration  curves  D,  E  and  H  of 
figure  1,  K  of  figure  2,  and  O  of  figure  3  these  periods  are  one 
hour,  one  hour  thirty  minutes,  six  hours,  two  hours,  and  one 
hour  thirty  minutes  respectively.  During  this  apparent  inhibi- 
tion there  is  a  rapid  decrease  of  hydrogen  ion  which  cannot  be 
accounted  for  by  the  decrease  caused  by  the  presence  of  suffi- 
cient orthophosphate  in  solution  at  that  time.  Even  after  the 
ortho  has  acquired  a  comparatively  high  concentration  the  de- 
crease is  not  accounted  for  by  it.  For  example  in  figure  1,  curve 
H,  there  is  a  decrease  of  .14  mole  of  hydrogen  ion  with  the  for- 

32 


33 


mation  of  but  .10  mole  of  orthophosphate,  in  E,  .13  mole  with 
.10  mole  orthophosphate,j  and  in  C,  .16  mole  of  hydrogen  ion 
with  the  formation  of  but  .10  mole  of  orthophosphate.  Other 
comparisons  show  similar  results. 

Furthermore,  if  we  plot  hydrogen  ion  concentration 
against  orthophosphate  in  each  solution  at  that  particular  time, 
a  set  of  curves,  for  example  from  solutions  D,  E,  and  H,  may 
be  obtained,  figure  7,  which  should  be  identical  with  curves  of 
the  same  HC1  concentration  plotted  from  data — table  17  and 
figure  6,  unless  other  influences  cause  a  decrease.  A  compari- 
son with  curves  plotted  from  data  in  table  17,  curves  in  figure 
6,  reveals  quite  a  difference  in  their  respective  slopes.  To  em- 


Hydrafion  and  Hydrogen  Ion  Concentration  Curves 
orSo/ution  K 

.3M.   NaP03 
.339  M.    HC2 


50  100 

Time  in  hours 


150  200 

I  Division  =25  Hours 


250 


FIGURE  2. 

phasize  this,  curves  of  figure  6  are  superimposed  on  curves  of 
figure  7.  See  figure  9.  Those  plotted  from  mono-sodium  phos- 
phate-hydrochloric acid  mixtures  are  steeper  than  the  ones 
obtained  from  actual  hydration.  The  latter  tend  to  become 
what  they  should  be  in  mono-sodium  phosphate-hydrochloric 
acid  mixtures  of  their  concentrations  as  the  reaction  tends 

34 


toward,  completion.  There  is,  therefore,  during  the  period  of 
apparent  inhibition  a  rapid  decrease  of  hydrogen  ion — a  re- 
action which  requires  time.  Also,  the  concentration  of  hydro- 
gen ion  is  much  less  than  we  should  expect  normally  in  solu- 
tions of  hydrochloric  acid  and  mono-sodium  phosphate  mix- 
tures of  the  same  concentration,  figure  9.  Furthermore  such 
differences  are  not  caused  by  sodium  monometaphosphate,  be- 
cause the  reaction  requires  time.  Experience  has  shown  that 
such  an  adjustment  of  equilibrium  would  be  attained  by  the 
time  the  solution  reached  the  temperature  of  the  bath  or  one- 
half  hour  provided  no  change  in  the  polymeric  condition  of  sod- 
ium monometaphosphate  occurs.  It  has  been  shown  by  the 
freezing  point  method  that  in  solution  sodium  trimetaphosphate 
changes  to  the  sodium  monometaphosphate  after  a  time1. 

Hydration  and '  Hydrogerrion  Concentration 
Curves  of  Solution  O 

J  M.NaPO3 
.339  M.  HC2 


20 

Time  in  hours 


40  60 

/  Division  -10  Hours 


60 


FIGURE  3. 


1  Holt  and  Meyers  J.  C.  S.,  Trans.  103,  1913,  532. 

35 


That  there  is  no  change  is  shown  by  the  preparation  of  a  hy- 
drate of  sodium  mononietaphosphate,  where  the  solution  was 
concentrated  till  it  separated.  It  is  the  hydrate  of  sodium 
mononietaphosphate  we  obtain  as  its  solution  behaves  like  the 
original  solution.  Therefore  it  does  not  seem  that  the  decrease 
of  hydrogen  ion  can  be  caused  by  the  unchanged  mononieta- 
phosphate. By  comparing  curves  made  from  actual  mixtures 
with  those  made  from  data  obtained  from  hydration  with  the 
same  hydrochloric  acid  concentrations  in  figure  9,  a  difference 
in  curve  .483  M.  HC1  of  .11  mole  of  hydrogen  ion  occurs  when 
.1  mole  of  orthophosphate  is  formed,  .07  with  .2  mole  of  ortho- 
phosphate,  .02  mole  with  .3  mole  of  orthophosphate,  .01  mole 
with  .4  mole  of  orthophosphate,  and  finally  when  the  reaction 
is  complete  the  difference  has  disappeared.  In  curves  .339  M. 
HC1  there  is  a  difference  of  .1  mole  hydrogen  ion  when  .1  mole 
orthophosphate  is  formed,  .07  mole  when  .2  mole  orthophos- 
phate is  formed,  and  .024  mole  when  .3  mole  of  orthophosphate 
is  formed,  .008  mole  when  .4  mole  of  orthophosphate  is  form- 
ed and  finally  at  completion  the  curves  are  identical. 

In  curve  of  .192  M.  HC1  these  differences  are  .046  and  .015 
moles  of  hydrogen  ion  with  the  formation  of  .1  mole  and  .2 
mole  of  orthophosphate  respectively.  The  curves  are  almost 
identical  in  other  concentrations  and  finally  identical  at  com- 
pletion. 

Since  there  is  a  decrease  of  this  difference  there  must  be  a 
decrease  of  the  cause  of  the  difference  in  their  respective  solu- 
tions. By  cross  comparisons  the  rate  of  formation  of  the  sub- 
stance which  causes  the  decrease  must  depend  upon  the  amount 
of  hydrogen  ion  in  solution.  Therefore  toward  the  end  of  all 
reactions  where  the  initial  substance  undergoing  the  reaction 
is  low  in  concentration  and  where  the  hydrogen  ion  is  low  there 
is  almost  no  difference — a  fact  which  indicates  the  lowering  of 
the  hydrogen  ion  due  almost  wholly  to  the  orthophosphate. 
In  the  very  low  acid  this  fact  is  evident  long  before  the  reac- 
tion has  reached  completion.  The  above  considerations  and 
the  period  of  apparent  inhibition  show  that  the  reaction  is  a 
two  stage  reaction  where  the  first  stage  decreases  and  the  last 
stage  overtakes  it.  Then  too  the  difference  in  higher  concen- 
trations of  hydrogen  ions  does  not  finally  disappear  until  the 

36 


reaction  is  almost  complete.  This  indicates  that  hydrogen  ion 
has  more  effect  upon  the  first  stage  of  the  reaction  than  the  last 
stage.  These  comparisons  were  made  in  .5  molar  solutions. 
Similar  results  are  obtainable  from  other  solutions. 

Now  since  pyrophosphate  was  actually  formed  during 
the  analysis  of  orthophosphate  and  since  in  table  18  measure- 
ments of  hydrogen  ion  have  been  made  in  solutions  of  hydro- 
chloric acid-pyrophosphate  mixtures  and  curves  plotted  in 
figure  8  which  show  the  decrease  of  hydrogen  ion  with  an  in- 

Hytfrat/on  ancf  tfycfrogen  Ion  Concentration 
Curves  of  Solutions  Z  &  Z-A 

.3  M.  A/a  PO3 
.01 M.     HC1 


Hydrogen  Ion  Concentration  fold)  Curve  ofZ.  and  21- 


40 
Time  in  Days 


/20  160 

/  Division  =  20  Day '$ 


FIGURE  4. 


crease  of  pyrophosphate  and  since  there  is  an  abnormal  de- 
crease in  hydrogen  ion  in  solutions  studied  excepting  S,  it  is 
evident  that  the  decrease  of  hydrogen  ion  during  the  hydra- 
tions  is  due  to  the  joint  effect  of  pyro  and  orthophosphates, 
and  from  the  above  it  seems  that  pyro  is  formed  as  an  inter- 
mediate product.  From  figures  6,  7,  8  and  9,  an  estimate  of 
the  amount  of  pyrophosphate  formed  may  be  made  by  ap- 
proximating the  amount  of  pyro  necessary  to  cause  the  ab- 

37 


normality  of  the  various  curves  in  figure  9.  In  solution  C, 
.5  M.  NaPO3  and  .483  M.  HC1  there  is  the  greatest  deviation. 
From  the  difference  of  hydrogen  ion  concentration  there  is  at 
least  .1  M.  of  Na2H2P2O7  (the  intermediate  product)  formed 
as  a  maximum.  Then  there  are  all  the  possible  concentra- 
tions existing  in  the  solution  between  this  upper  limit  and  zero 
as  the  difference  in  hydrogen  ion  becomes  progressively  less. 
Other  solutions  show  a  lower  value  for  their  upper  limits  de- 
pending on  the  initial  acid  and  NaPO3  concentrations. 


Hy d ration  &  Hydrogen  Ion 
Concentration  Curves  of 
S&S-A 

.3  M. 


0  50  100  150  200 

Time  in  D0ys  I  Division = 25  Do/s 

FIGURE  5. 


Now  as  to  the  period  of  apparent  inhibition,  it  is  not  likely 
that  if  pyrophosphoric  acid  is  formed  as  an  intermediate  prod- 
uct, that  the  hydration  of  pyro  to  orthophosphate  would  be 
delayed  while  the  pyro  built  to  a  certain  concentration  before  it 
began  the  second  stage  of  the  reaction.  It  seems  rather  that 
the  reaction  would  begin  just  as  soon  as  we  had  the  slightest 

38 


trace  of  pyro  in  solution.  In  other  words  at  the  beginning  of 
the  final  stage  of  the  reaction  the  velocity  would  be  zero  while 
the  initial  velocity  of  the  first  stage  would  be  a  maximum. 
Therefore  if  there  is  any  hydration  at  all  in  the  final  stage  the 
velocity  must  rise  to  a  maximum  and  decrease  to  zero  at  com- 
pletion. The  maximum  for  any  particular  solution  would  be 
when  the  relative  influence  of  the  hydrogen  ion,  which  is  de- 
creasing, is  counteracted  by  the  pyrophosphate  and  orthophos- 
phate  formed.  There  are  two  tendencies, — one  to  slow  up  the 
velocity  by  the  withdrawal  of  hydrogen  ion,  the  other  to  speed 
it  up  by  increasing  pyrophosphate. 

It  is  evident  then  that  the  acceleration  must  be  positive, 
pass  through  zero  and  become  negative.    This  then  means  a 


flycrogen  /on  Concentration 

in  different 

Mono  Sodium  Phosphate 

and 


Hydrochloric  /Jcid  Concentrations 


Concentration    NaH2  P04          I  division  - .  o5M. per  Liter 
FIGURE  6. 
39 


point  of  inflection  near  the  beginning  in  all  the  hydration 
curves.  In  solution  S,  figure  5,  it  has  been  experimentally 
shown  that  there  should  be  a  point  of  inflection  because  the 
hydration  curve  is  concave  toward  the  time  axis.  In  other 
curves  where  the  reactions  were  so  rapid  it  was  impossible  to 
secure  reliable  data  near  the  beginning.  In  S  since  these  reac- 
tions are  consecutive  and  since  we  started  with  very  low  hy- 
drogen ion  concentration  and  since  by  former  hydrations  we 
know  the  accelerating  effect  of  hydrogen  ion  upon  the  first 
stage  of  the  reaction  and  since  we  have  shown  by  measurement 
that  the  concentration  of  hydrogen  ion  increases  in  S  we  may 
therefore  conclude  that  as  the  concentration  of  hydrogen  ion 
increases  the  concentration  of  the  pyrophosphate  would  tend 
to  increase  and  as  the  concentration  of  the  pyrophosphate  tends 
to  increase  the  velocity  of  the  last  stage  of  the  reaction  would 
increase.  This  would  mean  a  positive  acceleration.  The  curve 
has  been  carried  out  sufficiently  to  show  that  it  has  a  positive 
acceleration.  Finally  this  curve  must  become  parallel  to  the 
time  axis  at  completion.  This  then  means  that  there  must  be 
a  point  of  inflection. 

TIME  RELATION  OF  HYDRATION  WITH  CONSTANT  NaPO3 
AND  CHANGE  OF  HC1. 

In  solutions  D,  E,  and  H,  tables  3,  4,  5,  6,  7,  and  8  and 
figure  1  and  their  duplicates  the  concentrations  of  the  NaPO3 
were  the  same,  .5  molar  initially  while  the  concentrations  of 
HC1  used  were  .483  M.  .339  M.  and  .192  M.  The  times  re- 
quired for  complete  hydration  were  185,  365,  and  975  hours  re- 
spectively. In  figure  1  it  is  shown  that  the  concentration  of 
hydrogen  ion  decreases  considerably  and  in  the  lower  acid 
concentration  it  was  relatively  smaller.  In  solution  D  the 
hydrogen  ion  was  finally  about  one-fourth  what  it  was  initially. 
In  solution  E  it  had  the  ratio  of  8  to  1.  In  solution  H  the  ra- 
tio was  about  16  to  1.  Final  concentration  depends  upon  the 
initial  concentration  of  the  hydrogen  ion  and  the  decrease  of 
concentration  of  hydrogen  ion  is  greater  as  the  initial  acid  con- 
centration is  less  to  a  point  nearing  the  concentration  of  hydro- 
gen ion  furnished  by  a  monosodium  phosphate  solution  of  the 
same  molar  concentration,  the  final  product  of  the  reaction. 

40 


In  solutions  K,  Z,  and  S  the  initial  concentration  of 
NaPO3  was  .3  molar  and  the  concentration  of  HC1  in  each  case 
was  .339  M.,  .010  M.,  and  OOOM.  The  times  required  for  com- 
plete hydration  were  260  hours,  175  days,  and  at  the  end  of 
200  days  S  was  49.14%  hydrated.  At  a  point  where  the  velocity 
was  at  maximum  in  S  figure  5  it  would  have  required  357  days 
to  complete  the  reaction  had  it  continued  uniformly  from  that 
point  to  completion.  So  at  a  minimum  it  would  require  at 
least  a  year  for  complete  hydration  of  a  .3  molar  aqueous  solu- 


— 1 1 1 1 1 T 

hydrogen  /on  Concentration 

Against 

Orthophosphote  Concentration 

From  Data  in  D,  E  andfi 


Concentration  /\faH2P04 

FIGURE  7. 


.3  .4  .5 

I  division  = .  o5M.  per  Liter 


tion  at  45°  C.  It  is  quite  probable  however  that  several  years 
would  be  required  because  the  velocity  gradually  decreases  as 
the  reaction  nears  completion.  In  solution  K  figure  2  the  hy- 
drogen ion  concentration  was  about  two-fifths  of  what  it  was 
initially.  The  ratio  in  solution  Z  was  26  to  1,  figure  4.  In 
solution  S  at  the  end  of  200  days  there  was  an  actual  increase 
of  hydrogen  ion  concentration  which  was  progressive  with 
time.  The  ratio  of  the  initial  concentration  to  the  final  meas- 


41 


urement  at  the  end  of  200  days  was  1  to  65.  The  concentra- 
tion of  the  hydrogen  ion  is  65  times  greater  at  the  end  of  200 
days  than  at  the  beginning.  It  may  be  pointed  out  here  too 
that  the  concentration  of  hydrogen  ion  at  this  point  is  consid- 
erably greater  than  the  concentration  of  hydrogen  ion  in  a 
solution  of  mono-sodium  phosphate  of  the  same  concentration — 
the  final  product  of  the  hydration.  The  concentration  measured 
at  the  end  of  200  days  was  4.18  x  10~5,  table  16,  while  that  in  a 


I 


ii        iii 

Hydrogen  Ion  Concentration  in 
Different  Sodium  Pyrophosphate 
8c  Hydrochloric  Acid  Concentrations 


I 


0  .OS  JO  .15  .20  .26 

Concentration     Ndz  ^2^2  °?      I  Division  *• .  025 'M.  per  Liter 

FIGURE  8. 

.3  M.  NaH2PO4  is  only  4.01  x  10-5,  table  17.  Now  since  we 
would  expect  a  hydrogen  ion  concentration  of  4.01  x  lO^5  from 
a  .3  Molar  aqueous  solution  of  NaPO3  when  it  is  completely 
hydrated,  this  is  another  indication  that  pyrophosphate  is  form- 
ed as  an  intermediate  product.  It  would  indicate  that  this  hy- 
drogen ion  concentration  in  S  should  go  through  a  maximum. 


42 


This  may  be  explained  from  the  pyrophosphate  formed  in  the 
solution.  From  the  third  ionization  constant  determined  re- 
cently1 we  obtain  an  hydrogen  ion  concentration  of  1  x  10~4 
moles  per  liter  for  a  .3  M.  Na2H2P2O7  solution.  By  actual 
measurement  at  45°  C.  of  .2  molar  solution  1.71  x  10"4  is  ob- 
tained, a  concentration  four  times  as  great  as  the  last  concentra- 
tion measured  in  solution  S.  Furthermore  for  a  given  initial 
concentration  of  sodium  monometaphosphate  there  should  be 
an  initial  concentration  of  hydrogen  ion  which  would  remain 
invariable  throughout  the  entire  hydration,  because  in  higher 
acid  concentrations  there  is  a  decrease  of  hydrogen  ion  and  in 
very  low  concentrations  there  is  an  increase.  Therefore  there 


..3 


.2 


\ 


\ 


I  I  I  I  I 

Curves  of  Figure  6 
Superimposed  on  Figure  7 


°  From  Fig.  6 

• •From  Fy.  7 


0  ./  .2  .3  .4  .S 

Concentration  ofNafy  P04  ~IDiv.=.  c5M.  per  Liter 
FIGURE  9. 


iKolthoff,  Pharm.  Weekblad  57,  474  Chemical  Abstracts,  Volume  14 
No.  20,  3011. 

43 


must  be  some  concentration  of  hydrogen  ion  where  there  would 
occur  neither  an  increase  nor  a  decrease  for  each  initial  sodium 
monometaphosphate  solution.  From  data  in  tables  14  and  16 
figures  4  and  5,  curves  Z  and  S,  for  a  .3  M.  NaPO3  solution  this 
concentration  of  hydrogen  ion  must  lie  between  3.62  x;  10~* 
and  4.18  x  10~5  moles  per  liter.  At  these  initial  hydrogen  ion 
concentrations  the  influence  of  the  concentration  of  sodium 
monometaphosphate  upon  the  rate  of  hydration  could  be  ac- 
curately studied  without  a  change  of  hydrogen  ion. 


The  curves  appearing  in  this  article  were  prepared  from 
tracings  made  by  Mr.  S.  J.  Ballard,  draftsman  of  the  Depart- 
ments of  Chemistry  and  Chemical  Engineering. 


SUMMARY 


1.  A  definite  polymer,  sodium  monometaphosphate,  has 
been  prepared  and  its  hydration  studied.    A  twofold  method 
was  employed  to  follow  the  hydration ;  first,  the  amount  trans- 
formed to  the  orthophosphate  was  separated  and  determined 
as   orthophosphate  by  the   standard   magnesium   ammonium 
phosphate  method,   second,   the   hydrogen  ion   concentration 
was  measured  concurrently  with  the  determination  of  ortho- 
phosphate. 

2.  The  hydrogen  ion  concentration  decreased  progres- 
sively with  time  except  in  the  .3  Molar  NaPO3  solution  where 
the  hydrogen  ion  of  the  aqueous  solution  was  not  supplemented 
by  additional  acid.    Here  there  is  an  increase  which  tends  to 
reach  a  point  in  concentration  to  which  the  higher  concentra- 
tions tend.     This  concentration  lies  between  4.18  x  10~5  and 
3.62  x  10~4  Moles  of  hydrogen  ion  per  liter,  experimentally  de- 
termined in  Tables  14  and  16. 

3.  Pyrophosphoric  Acid  was  formed  as  an  intermediate 
product.     Its  presence  was  established  during  the  determina- 
tion of  orthophosphate.    It  was  confirmed  by  the  abnormal  de- 
crease of  hydrogen  ion  in  solutions  in  process  of  hydration. 
That  it  is  an  intermediate  product  is  indicated  from:  (1)  ab- 
normalities of  hydrogen  ion  concentration  shown  in  phosphate- 
hydrochloric  acid  curves,  figure  9 ;  (2)  period  of  apparent  inhi- 
bition ;   (3),  tendency  in  solutions  of  very  low  hydrogen  ion 
concentration  to  exhibit  a  point  of  inflection  in  their  hydration 
curves,  experimentally  shown,  figure  5 ;    (4)  the  increase  of 
the  concentration  of  hydrogen  ion  in  aqueous  solutions  above 
that  of  the  same  concentration  of  a  mono-sodium  phosphate 
solution  (the  final  product  of  the  reaction)  long  before  the  re- 
action is  complete.    This  apparently  settles  a  question  in  dis- 
pute since  the  time  of  Graham  in  1833. 

4.  The  times  required  for  complete  hydration  for  a  .5  M. 
NaPO3  solution  with  .483  M.,   .339  M.,  and  .192  M.  HC1  were 
185,  365,  and  975  hours  respectively.    For  a  .3  molar  solution 

45 


of  NaPO3  the  times  required  respectively  for  completion  with 
.339  M.,  .010  M.,  and  .000  M.  HC1  were  260  hours,  175  days,  and 
200  days  for  49.14%  hydration — a  fact  which  indicates  several 
years  for  completion. 

When  the  initial  concentration  of  hydrochloric  acid  was 
.339  M.  in  each  case  the  times  required  to  complete  the  reaction 
were,  respectively,  for  a  .5  M.,  .3  M.,  and  a  .1  M.,  NaPO3,  365, 
260,  and  70  hours. 

Seven  different  hydrations  were  run  in  all.  Duplicates 
were  obtained  from  the  five  which  ran  rapidly,  and  duplicate 
samples  were  taken  in  the  very  slow  ones.  The  seven  repre- 
sent 3  different  NaPO3  concentrations  and  4  different  initial 
HC1  concentrations. 

5.  The  decrease  of  hydrogen  ion  caused  jointly  by  the 
orthophosphate  and  pyrophosphate  complicates  the  reaction. 
From  the  conduct  of  the  solutions  in  which  hydration  occurred 
the  reaction  seems  to  take  place  in  two  stages,  the  first  of  which 
is  effected  more  by  hydrogen  ion.  The  behavior  of  solutions  of 
very  low  hydrogen  ion  concentration  in  exhibiting  a  tendency 
to  show  a  point  of  inflection  and  those  of  higher  hydrogen  ion 
concentration  to  show  a  period  of  apparent  inhibition  in  their 
respective  hydration  curves  seems  to  indicate  that  these  reac- 
tions are  consecutive  and  not  concurrent.  The  hydration  of 
sodium  monometaphosphate  is,  therefore,  by  molecular  for- 
mula, expressed: 

2NaP03  +  H20  -»  Na2H2P207  +  H2O  -»  2NaH2PO4 . 


46 


VITA. 

Samuel  J.  Kiehl  was  born  in  Sewickley  Township,  West- 
moreland County,  Pennsylvania,  May  16,  1883.  He  graduated 
from  Otterbein  College,  Westerville,  Ohio,  in  1910,  where  he 
taught  the  year  before  and  the  three  years  following  gradua- 
tion. In  1913  he  began  teaching1  in  the  West  High  School, 
Columbus,  Ohio.  He  left  West  High  School  in  1917  to  become 
an  instructor  in  the  Department  of  Chemistry,  Columbia  Uni- 
versity, a  position  he  has  held  to  date.  While  he  was  teaching 
in  Otterbein  and  Columbus  he  was  a  graduate  student  at  the 
Ohio  State  University.  He  was  a  graduate  student  in  the  De- 
partment of  Chemistry,  Columbia  University,  during  the  sum- 
mers of  1915,  1916,  and  1917,  and  during  the  years  1917-18, 
1918-19,  1919-20,  and  1920-21. 


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